A total of 20 boys completed this randomized 9-week, placebo-controlled, double-blind comparison of methylphenidate (MPH; Ritalin) and dextroamphetamine (DEX, Dexedrine) on tic severity in boys who have both attention-deficit/hyperactivity disorder (ADHD) as well as the tic disorder known as Tourette's syndrome. Relatively high doses of MPH and DEX produced significant increases in tic severity, but these were not generally sustained on Ritalin. Overall, 14 of 20 subjects continued stimulant treatment for 1 to 3 years, generally in combination with other medicines. Stimulant-associated adverse effects, including tic exacerbations, were reversible in all cases. The majority experienced improvement in ADHD symptoms with acceptable effects on tics. MPH was better tolerated than DEX.